1. Field of the Invention
The present invention provides for a method of more stably and efficiently expressing transgenes in a cell. The present invention also provides a mammalian host cell that harbors VP16-CREB gene construct in its genome.
2. Description of the Background
Protein therapeutics has several advantages over conventional small molecule drugs. Because protein therapeutics generally works with improved specificity, they are less likely to interfere with normal biological processes and cause adverse effects. Proteins are also less prone to immune responses by human body than chemical drugs. These and other related benefits makes protein therapeutics to be one of the fastest growing segments in pharmaceutical industry.
Protein therapeutics, including antibody therapeutics, is produced using recombinant DNA technology in organisms such as bacteria, yeast, insect cells, and animal cells. For protein therapeutics, the gene coding for the protein is introduced into the host cells and the therapeutic proteins produced from the introduced gene are recovered from the host cells. By far, animal cells have been the most preferred host as they are capable of performing complex modifications to the proteins required for the desired function.
In most cases, protein therapeutics production from animal cells is carried out first by introducing the gene for therapeutics into the host cells. In most cases, a single cell that stably incorporates the gene into its own genome is selected and grown into a cell line for the production. Although several different types of animal cells have been used as host cells, Chinese Hamster Ovary (CHO) cells have been the most widely used.
Large scale production of protein therapeutics in animal cells, such as CHO cells, is technically demanding due to the low level of efficiency. In order to overcome this set back, people have used a derivative of CHO cells such as DG44 which is deficient in dihydrofolate reductase expression. In DG44 cell system, a genetic selection pressure is applied so that the stably incorporated transgenes can be amplified. The overall amount of therapeutic proteins produced from gene-amplified DG44 cells becomes increased simply because there are more copies of the gene available inside the cells.
However, the use of DG44 cells has a major drawback because of the lack of stability of amplified genes. Cell lines generated for recombinant therapeutics proteins using DG44 cells with gene amplification can show sudden decrease in the productivity during the large scale production process, due to the instability of the amplified genes. As the process of gene amplification itself is time consuming, this type of added delay can cause a significant delay in the overall processing time with a potential for a significant financial loss.
This clearly indicates that there is a need in the industry for an alternative and improved cell line to be used as a host for protein therapeutics production. In the present application, we report development of genetically engineered CHO cells that are capable of producing therapeutics protein at higher levels than the original CHO cells, and also show improved growth characteristics, making them suitable host for scale-up protein therapeutics manufacturing.